How to choose the right sized turbine housing?

Turbine housing is one of the essential parts on a turbocharger. If you have a difficulty choosing the “right” sized turbine housing, here’s a brief introduction and guideline for you.

Before we start, let’s cover some basics. A turbocharger has two sections, turbine housing is on the hot side. Exhaust gasses flow from the engine into the turbine housing inlet, through the passage causing the wheel assembly to spin; therefore it must be able to endure high temperature. Usually a certain percentage of Inconel is added to its composition to ensure its durability, percentage varies according to engine bay configuration.

Besides universal type turbochargers, Arashi also offers quite many bolt on turbochargers, therefore there are quite a few turbine in flanges which you need to make sure the one you choose matches with the manifold you select. Same applies to turbine outlet, you must make sure it matches with the downpipe.

Once settled on the connecting area, back to our main discussion of what sized turbine housing should you choose for your turbo. There are two types of sizing for turbine housing we currently offer, one of them in A/R and the other one in cm². A/R means area/radius, larger A/R turbine housing means more flow while smaller A/R turbine housing spools better.

Compared to larger A/R housing, smaller A/R housing exhaust gas fills up the passage faster and thus spins the wheel at lower engine RPMs, leading to quicker spool. On the contrary, bigger A/R housing takes longer to boost up, but it offers better high-RPM power.

When your turbo has excessive backpressure, that means you need to increase your A/R size as the passage is not big enough to flow the exhaust gas fast enough, replacing a bigger A/R housing will also allow your application to make more power. However, if you find your turbo running with spool lags and you’d like to improve it, changing to a smaller A/R housing would be a better alternative for you.

Choosing the right sized turbine housing might not impact your performance greatly, but it is essential in keeping your set up smooth.